From Book One 

Oh you may not think I'm pretty,
But don't judge on what you see,
I'll eat myself if you can find
A smarter hat than me.
You can keep your bowlers black,
Your top hats sleek and tall,
For I am the Hogwarts Sorting Hat
And I can cap them all.
There's nothing hidden in your head
The Sorting Hat can't see,
So try me on and I will tell you
Where you ought to be.
You might belong in Gryffindor,
Where dwell the brave at heart,
Their daring, nerve, and chivalry
Set Gryffindors apart;
You might belong in Hufflepuff,
Where they are just and loyal,
Those patient Hufflepuffs are true
And unafraid of toil;
Or yet in wise Ravenclaw,
If you've a ready mind,
Where those of wit and learning
Will always find thier kind;
Or perhaps in Slytherin
You'll make your real friends,
Those cunning folk use any means
To achieve their ends.
So put me on! Don't be afraid!
And don't get in a flap!
You're in safe hands (though I have none)
For I'm a Thinking Cap! 

From Book Four 
A thousand years or more ago,
When I was newly sewn,
There lived four wizards of renown,
Whose names are still well known:
Bold Gryffindor, from wild moor,
Fair Ravenclaw, from glen,
Sweet Hufflepuff, from valley broad,
Shrewd Slytherin, from fen.
They shared a wish, a hope, a dream,
They hatched a daring plan
To educate young sorcerers 
Thus Hogwarts School began.
Now each of these four founders
Formed their own house, for each
Did value different virtues
In the ones they had to teach.
By Gryffindor, the bravest were
Prized far beyond the rest;
For Ravenclaw, the cleverest
Would always be the best;
For Hufflepuff, hard workers were
Most worthy of admission;
And power-hungry Slytherin
Loved those of great ambition.
While still alive they did divide
Their favorites from the throng,
Yet how to pick the worthy ones
When they were dead and gone?
'Twas Gryffindor who found the way,
He whipped me off his head
The founders put some brains in me 
So I could choose instead!
Now slip me snug about your ears,
I've never yet been wrong,
I'll have a look inside your mind
And tell where you belong! 

From Book Five
In times of old when I was new
And Hogwarts barely started
The founders of our noble school
Thought never to be parted:
United by a common goal, 
They had the selfsame yearning, 
To make the world's best magic school
And pass along their learning.
"Together we will build and teach!" 
The four good friends decided
And never did they dream
That someday they might be divided,
For were there such friends anywhere
As Slytherin and Gryffindor?
Unless it was the second pair
Of Hufflepuff and Ravenclaw?
So how could it have gone so wrong?
How could such friendships fail?
Why, I was there and so can tell 
The whole sad, sorry tale.
Said Slytherin, "We'll teach just those
Whose ancestory is purest."
Said Ravenclaw, "We'll teach those whose
Intelligence is surest."
Said Gryffindor, "We'll teach all those
With brave deeds to their name."
Said Hufflepuff, "I'll teach the lot, 
And treat them just the same."
These differences caused little strife
When first they came to light,
For each of the four founders had
A House in which they might
Take only those they wanted, so, 
For insistance, Slytherin, 
Took only pure-blood wizards 
Of great cunning, just like him, 
And only those with sharpest mind 
Were taught by Ravenclaw
While the bravest and the boldest 
Went to daring Gryffindor.
Good Hufflepuff, she took the rest,
And taught them all she knew, 
Thus the Houses and their founders
Retained friendships firm and true. 
So Hogwarts worked in harmony
For several happy years, 
But then discord crept among us
Feeding on our faults and fears.
The Houses that once, like pillars four,
Had once held up our school, 
Turned upon each other and, 
Divided, saught to rule. 
And for awhile it seemed the school 
Must meet an early end,
What with dueling and with fighting
And the clash of friend on friend
And at last there came a morning 
When old Slytherin departed
And though the fighting then died out, 
He left us quite downhearted.
And never since the founders four 
Were whittled down to three
Have the Houses been united
As they once were meant to be.
And the Sorting Hat is here
And you all know the score:
I sort you into Houses,
Because that is what I'm for,
But this year I'll go further, 
Listen closely to my song:
Though condemned I am to split you,
Still I worry that it's wrong, 
Though I must fulfill my duty
And must quarter every year
Still I wonder if sorting 
May bring the end I fear.
Oh, know the perils, read the signs, 
The warnings history shows, 
For our Hogwarts is in danger 
From external, deadly foes
And we must unite inside her,
Or we'll crumble from within
I have told you, I have warned you...
Let the Sorting now begin.